The general type and operating principles of PSA and VPSA, which are well known, are described, for example, in U.S. Pat. Nos. 3,564,816; 3,636,679; 3,717,974; 4,802,899; 5,531,807; 5,755,856; 5,871,564; 6,524,370; and 6,764,534, among others. Both PSA and VPSA apparatus may include one or more adsorbers, each having a fixed sieve bed of adsorbent material to fractionate at least one constituent gas from a gaseous mixture by adsorption into the bed, when the gaseous mixture from a feed stream is sequentially directed through the adsorbers in a co-current direction. While one adsorber performs adsorption, another adsorber is simultaneously purged of its adsorbed constituent gas. In a PSA apparatus, the purging is performed by part of the product gas being withdrawn from the first or producing adsorber and directed through the other adsorber in a counter-current direction. In a VPSA apparatus, the purging primarily is performed by a vacuum produced at the adsorber inlet to draw the purged gas from the adsorber. Once the other adsorber is purged, the feed stream at a preset time is then directed to the other adsorber in the co-current direction, so that the other adsorber performs adsorption. The first adsorber then is purged either simultaneously, or in another timed sequence if there are more than two adsorbers, all of which will be understood from a reading of the above described patents.
When, for example, such apparatus is used to produce a high concentration of oxygen from ambient air for use in various applications, whether medical, industrial or commercial, air which enters the apparatus typically contains about 78% nitrogen, 21% oxygen, 0.9% argon, and a variable amount of water vapor. Principally, most of the nitrogen is removed by the apparatus to produce a gas product, which for medical purposes, for example, typically may contain at least about 80% oxygen. Most such apparatus for medical uses generally are too bulky for use by patients who are traveling or otherwise wish to leave their home environments for any purpose. In those cases, patients will normally forego the use of oxygen concentrators and revert to the use of pressurized oxygen tanks. While oxygen tanks have been very useful in enabling patients to be more ambulatory, they nevertheless are restricted in use, as for example because of limited oxygen storage capacity or because their use may be prohibited in certain modes of public. transportation or locations where flammable materials can create a hazard. Although the useful life of oxygen tanks may be extended by the use of oxygen concentration devices (“OCD”), as disclosed, for example, in co-owned U.S. Pat. No. 6,427,690, McCombs et al., issued Aug. 6, 2002, their use nevertheless continues to be problematic because of safety and storage concerns, access to re-supplies of oxygen, and continuing medical expenses and reimbursement paperwork for the oxygen.
There having been developed a particularly useful and highly portable oxygen concentrator used for medical purposes and operating on PSA principles as disclosed in co-owned U.S. Pat. No. 6,764,534, McCombs et al., issued Jul. 20, 2004, the entire disclosure of which is incorporated by reference, the present invention builds on that knowledge by an even more compact, lighter weight and very highly portable oxygen concentrator for medical uses.
As is now well known, the most effective use of inhaled oxygen occurs at the onset of inhalation, and various devices have been constructed to deliver oxygen from pressurized oxygen tanks only when inhalation is first sensed by the devices and only during the initial stage of the inhalation cycle. U.S. Pat. No. 6,764,534, for example, discloses a system that primarily only delivers oxygen at the initial stage of inhalation by detecting a drop in pressure as sensed by inhalation of a user through a conventional cannula (not shown) to actuate a transducer circuitry causing a flow control valve to be opened for a predetermined time and allow a predetermined amount of the oxygen enriched gas to be delivered to the user in oxygen concentrations up to about 95%.